This article showed that the Physico-chemical properties of bone substitute materials have an impact on the degradation process. The findings are in line with the literature. The design of the study was well adapted to the aim. The main contribution of the study is that sintering temperature has an impact on the Physico-chemical properties of natural HA and the degradation process. However, it is known from general material research that the temperature of sintering impacts material properties. The overall strength of the article is the detailed presentation of the mechanical and microstructural properties of the two xenograft materials. The study will be a reference guide for the deployment of the Sinus Lift process. The study is good for publication if the under-listed points are attended to.

Major points for revision.

1. The methodology should be written before results and discussion else authors should justify why results came first.
2. The use of ‘in the present study’ in paragraphs 1, 3, 5 should be replaced with something else to avoid the repetition.
3. Generally, on the discussion, the use of personal pronouns in statements such as ‘we observed’ (line 4 paragraph 3 page 8) should be discarded instead use ‘it was observed’
4. The reference section should be re-looked for inconsistency.

Minor points for revision. . 1. The background to the study was well written. Line 1 paragraph 3, page 3 needs to re-worded. 2. Figures 1 and 2 pages 3 and 4 respectively should be revisited, images seem not to be full. 3. Figure 6 on page 7, images for P and Ca are blur